const searchForm = document.getElementById('search-form');
const searchInput = document.getElementById('search-input');
const statusEl = document.getElementById('status');
const resultsEl = document.getElementById('search-results');
const resultsList = document.getElementById('results-list');
const graphContainer = document.getElementById('graph-container');
const infoPanel = document.getElementById('info-panel');
const infoContent = document.getElementById('info-content');

let network = null;

function showStatus(msg, isError = false) {
    statusEl.textContent = msg;
    statusEl.className = isError ? 'error' : 'loading';
}

function clearStatus() {
    statusEl.textContent = '';
    statusEl.className = '';
}

function escapeHtml(text) {
    const div = document.createElement('div');
    div.textContent = text;
    return div.innerHTML;
}

function formatAuthors(authors, maxLen = 3) {
    if (!authors || authors.length === 0) return 'Unknown';
    const names = authors.map(a => a.name || 'Unknown');
    if (names.length > maxLen) {
        return names.slice(0, maxLen).join(', ') + ' et al.';
    }
    return names.join(', ');
}

function showResults(papers) {
    resultsList.innerHTML = '';
    resultsEl.classList.remove('hidden');
    graphContainer.innerHTML = '';
    infoPanel.classList.add('hidden');

    papers.forEach(paper => {
        const li = document.createElement('li');
        const authors = formatAuthors(paper.authors);
        li.innerHTML = `
            <strong>${escapeHtml(paper.title || 'Untitled')}</strong>
            <span>${escapeHtml(authors)} — ${paper.year || 'n.d.'} — Citations: ${paper.citationCount || 0}</span>
        `;
        li.addEventListener('click', () => {
            resultsEl.classList.add('hidden');
            loadGraph(paper.paperId);
        });
        resultsList.appendChild(li);
    });
}

async function search(query) {
    showStatus('Searching...');
    try {
        const res = await fetch(`/api/search?q=${encodeURIComponent(query)}`);
        const data = await res.json();
        clearStatus();
        if (data.error) throw new Error(data.error);
        if (!data.papers || data.papers.length === 0) {
            showStatus('No papers found.', true);
            return;
        }
        showResults(data.papers);
    } catch (err) {
        showStatus(err.message, true);
    }
}

async function loadGraph(paperId) {
    showStatus('Loading reference graph...');
    try {
        const res = await fetch(`/api/graph/${encodeURIComponent(paperId)}`);
        const data = await res.json();
        clearStatus();
        if (data.error) throw new Error(data.error);
        renderGraph(data);
    } catch (err) {
        showStatus(err.message, true);
    }
}

function renderGraph(graph) {
    graphContainer.innerHTML = '';
    infoPanel.classList.add('hidden');

    const container = document.createElement('div');
    container.id = 'graph';
    graphContainer.appendChild(container);

    if (graph.nodes.length <= 1) {
        container.innerHTML = `
            <div class="empty-graph">
                <p><strong>No references found in OpenAlex for this paper yet.</strong></p>
                <p>This often happens with very recent preprints — OpenAlex hasn't ingested the reference list.</p>
            </div>
        `;
        const nodes = new vis.DataSet(graph.nodes);
        const edges = new vis.DataSet(graph.edges);
        const options = { nodes: { shape: 'dot', color: '#ff6b6b' } };
        network = new vis.Network(container, { nodes, edges }, options);
        return;
    }

    const nodes = new vis.DataSet(graph.nodes);
    const edges = new vis.DataSet(graph.edges);

    const options = {
        nodes: {
            shape: 'dot',
            scaling: {
                min: 10,
                max: 60,
                label: { enabled: true, min: 12, max: 22 }
            },
            font: { size: 14, color: '#333' }
        },
        edges: {
            width: 1,
            color: { color: '#888', highlight: '#000' },
            arrows: { to: { enabled: true, scaleFactor: 0.5 } },
            smooth: { type: 'continuous' }
        },
        groups: {
            seed: { color: '#ff6b6b' },
            reference: { color: '#45b7d1' }
        },
        physics: {
            stabilization: false,
            barnesHut: {
                gravitationalConstant: -3000,
                centralGravity: 0.3,
                springLength: 150,
                springConstant: 0.04,
                damping: 0.09
            }
        },
        interaction: {
            hover: true,
            tooltipDelay: 200
        }
    };

    network = new vis.Network(container, { nodes, edges }, options);

    network.on('click', (params) => {
        if (params.nodes.length > 0) {
            const nodeId = params.nodes[0];
            const node = nodes.get(nodeId);
            showNodeInfo(node);
        }
    });

    network.on('doubleClick', (params) => {
        if (params.nodes.length > 0) {
            const nodeId = params.nodes[0];
            loadGraph(nodeId);
        }
    });
}

function showNodeInfo(node) {
    infoPanel.classList.remove('hidden');
    infoContent.innerHTML = `
        <h3>${escapeHtml(node.label)}</h3>
        <p><strong>Authors:</strong> ${escapeHtml(node.authors)}</p>
        <p><strong>Year:</strong> ${node.year || 'n.d.'}</p>
        <p><strong>Citations:</strong> ${node.citationCount}</p>
        <button id="recenter-btn">Re-center graph on this paper</button>
        <p><em>Tip: you can also double-click a node to re-center.</em></p>
    `;
    document.getElementById('recenter-btn').addEventListener('click', () => {
        loadGraph(node.id);
    });
}

searchForm.addEventListener('submit', (e) => {
    e.preventDefault();
    const query = searchInput.value.trim();
    if (query) search(query);
});